The vast majority of research regarding the Stroop task has focused on why facilitation and interference occur. Relatively little research has addressed individual differences on this task (MacLeod, 1991). The research that has been conducted on individual differences with the Stroop task has primarily examined sex, age, hemispheric differences, and language. A clear trend has been found for age differences and the level of reading skill; interference is minimal for children in the first grade and gradually increases through second and third grades (Schiller, 1966). Preston and Lambert (1969) and Dyer (1971a) found interference between the two languages of bilinguals, but not to the same magnitude of within language interference. Block (1993) found significant correlation between Scoop effect and level of impulsivity in boys.
Both inattention and impulsivity are inhibiting factor in learning which receives wide attention due to its close relationship to arousal emotions, anxiety and motivation (Clark & Fiske, 1982; Mandler, 1984). Usually in situations that demand precise decision, judgement, fast reaction time - for example, tests and examinations - inattention and impulsivity can impair performance. Stroop tests are used to measure individual differences in attention, and it is used to differentiate between normal adults and adults with ADHD.
The experiment utilises two versions of Stroop test; Stroop 1 presents coloured meaningless letter string (xxx), Stroop 2 contains colour-words in incongruent colour print, both letter strings and colour-words were presented in rows on different sheets of A4 paper. The researcher seeks support to four hypotheses, which assume that there is a significant association between the performance on Stroop 1 test and the the two personality traits (impulsivity and inattention); also there is a relationship between Stroop 2 test performance and the two personality traits.
Method
Subjects
Fifty-four (54) students – comprising forty-two (42) females and twelve (12) males – from the University of Surrey took part in this experiment with an age range between 18 and 47 years and the mean age of 20.98 years. All subjects had normal or corrected to normal visual acuity and normal colour vision.
Materials
Three materials were used; Stroop 1 task, Colour-word Stroop 2 and a NEO-FFI Personality Traits Questionnaire. Both Stroop 1 and Colour-word Stroop 2 were colour-naming tasks. In Stroop 1 triple x (xxx) were intermittently presented in seven different ink colours in rows on a sheet of A4 paper. The subjects were timed with stop watches how quickly they could name the colours correctly. In Stroop 2 colour-words (e.g., BLUE) incongruent with the colour print (e.g., red) were presented and the participants were timed how quickly they could name the colour of the words. The words were presented in rows on an A4 sheet of paper. Another measure was taken from the NEO-FFI Personality Traits Questionnaire. Participants were asked to answer the questions which were related either inattention or impulsivity. Statements such as ‘I am forgetful in my daily activities’ relate to the personality traits of inattention and statements such as ‘I do things without thinking’ relate to the trait of impulsivity. There were 29 statements in total, 15 statements relating to inattention and 14 to impulsivity. The statement were rated individually by the participants on a six-point Linkert’s scale; 1 - Disagree strongly; 2 - Disagree; 3 - Disagree more than agree; 4 – Agree more than disagree; 5 - Agree and 6 – Agree strongly.
Design
The experiment used correlational design to explore the relationships among performance on Stroop tasks and scores taken from self-report questionnaires for the personality traits of impulsivity and inattention.
Procedure
Firstly, the participants worked in pairs; one of them undertook the task whilst the other timed the partner’s performance, then they exchanged roles. The first condition was the Stroop 1 task, in which ‘xxx’ signs were intermittently presented in seven different ink colours. Subjects were timed with stop watches how quickly they could name the colours correctly. Next the Stroop 2 condition was presented, in which colour-words incongruent with the colour print were presented and the participants were timed how quickly they could name the colour of the words. By the end of the first part of this experiment each participant had two times with millisecond accuracy.
Secondly, the participants were asked to work alone and fill out the NEO-FFI Personality Traits Questionnaire. Participants used a 1-6 scoring scale to rate each statement, which were related to either inattention or impulsivity. At the end, participants were asked to add up their scores given to certain question numbers, therefore they all gained two score numbers, one for inattention and one for impulsivity.
The data was analysed by SPSS using the parametric Pearson’s r and the non-parametric Spearman’s Rho.
Results
Prior to the correlational analysis of data certain descriptive statistical analysis were conducted and demonstrated on histograms to observe the nature of the underlying sampling distribution in the cases of each of the four variables. Both Stroop 1 and Stroop 2 conditions showed considerable skewness due to two outliers. As the population of the sample is small (54) and both scores were inexplicably low, to avoid counter-productive distortion, the scores of these two participants' were taken out of the data set. Following this, descriptive statistics were used again to obtain values for skewness and kurtosis and decide on the nature of the underlying sampling distributions for the variables.
x The distribution departs considerably from normal
Table 1. The values of skewness and kurtosis of the sampling distribution in the cases of the four variables.
This experiment aimed to use the Pearson’s r test to find correlation between the variables. Person’s r only can be used if the underlying sampling distribution is normal. All variables showed normal distribution, except the Stroop 2 variable, which is a non-Gaussian distribution. This assumption was drawn from the obtained value of skewness (0.724), as it is greater than twice the value of its standard error (0.330). In conclusion, the non-parametric Spearman's rho is used to investigate the correlation between Stroop 2 and the two personality traits and Person's r is used to find the correlation between Stroop 1 and the two personality traits.
x Correlation is significant at the 0.05 level (2-tailed).
Table 2. The results of bivariate correlations testing for correlations between the two Stroop tests and the two personality factors.
Hypothesis 1. There is a relationship between Stroop 1 performance and the inattention score. A slow time in the Scoop condition is related to high inattention score, and fast colour-naming ability is related to low inattention score.
Students' fast colour-naming ability was significantly associated with the personality factor of inattention and the correlation was positive. r = 0.30, p < 0.05. Colour-naming ability shared a low, 9% variance with inattention.
Hypothesis 2. There is a relationship between Stroop 1 performance and the impulsivity score. A slow time in the Scoop condition is related to high impulsivity score, and fast colour-naming ability is related to low impulsivity score.
Students' fast colour-naming ability was non-significantly associated with the personality factor of impulsivity. r = 0.028, p = 0.84. Colour-naming ability shared an insignificant, 0.078% variance with impulsivity.
Hypothesis 3. There is a relationship between the performance in the Stroop 2 interference task and the inattention score. A slow time in the Scoop interference condition is related to high inattention score, and fast colour-naming of colour-words is related to low inattention score.
Students' fast colour-words colour-naming ability was non-significantly associated with the personality factor of inattention. r = 0.25, p = 0.07. Colour-words colour-naming ability shared a low, 6.25% variance with inattention.
Hypothesis 4. There is a relationship between the performance in the Stroop 2 interference and the impulsivity score. A slow time in the Scoop condition is related to high impulsivity score, and fast colour-naming of colour-words is related to low impulsivity score.
Students' fast colour-words colour-naming ability was non-significantly associated with the personality factor of impulsivity. r = 0.17, p = 0.23. Colour-words colour-naming ability shared an insignificant, 2.89% variance with impulsivity.
Although there was no statement in concern with the relation between the two Stroop tests, it is still important to mention that there was a highly significant correlation between the two conditions, and the association was positive and linear. r = 0.68, p < 0.001. The colour-naming task shared the most, but still low variance with the interfering colour-words colour-naming task - sharing 46.2%.
Relationship between the performances
in Stroop 1 and Stroop 2
Figure 1. Scatterplot shows a positive linear association between the performance in the Stroop 1 and the Stroop 2 conditions.
Relationship between
Stroop 1 and Inattention
Figure 2. Scatterplot shows a positive linear association between the performance in the Stroop 1 condition and the Inattention score.
Discussion
This experiment was a correlational design, which is very limited in many ways. It only detects linear relationship, and only shows if two variables are associated, but cannot say that one causes the other. The result of the inferential tests only supported the Hypothesis 1, in Hypothesis 2, 3, and 4 was found non-significant relationships between the variables. In other words, there is a significant positive association between the colour-naming ability of meaningless letter string, which was measured in the Stroop 1 task and the personality factor of inattention. Although the Stroop 1 task seems to be a straightforward cognitive process, in which the colour is recognised and called out, in the task a full page of the letter strings were presented in rows. The performance on this task was measured by timing the participants how quickly they could name all the colours on the page. For a good performance on this monotonous task a quick reaction time in naming the colours was not enough, the participant had to show a consistently fast colour-naming tendency all the way through the task. In consequence, those subjects, with relative high inattention score gained slower time on the Stroop test.
A question arises from this finding. If Stroop 1 and Stroop 2 test highly correlated (p < 0.001), and Stroop 1 is associated with inattention, why Stroop 2 did not show significant correlation to this personality trait. Is this happened because the two tasks require different skills and ability to perform well; or the confounding and random variables influenced more the performance on the second task? For a good performance on the Stroop 2 task, beyond doubt, a more complex ability was required. Good selective attention was determining, as an accomplished reader cannot avoid reading and processing words, when looking at them. This information processing is automatic, fast and unconscious, also makes no demands on attention (Eysenck and Keane 1995). The ability to inhibit this automatic process and only pay attention of the colour of the word goes far beyond than just one cognitive ability. To complite well this task, abilities must have been involved, such as problem solving, vision restriction, controlled attention, and others. In conclusion, not only those required longer time to complete Stroop 2 task, who scored higher on inattention, but those as well, who’s capability on the other factors involved were lower. Therefore inattention itself cannot indicate a slower performance on Stroop 2 task. Despite the finding of a previous study (Block, 1993), which showed significant relationship between Stroop 2 test performance and impulsivity, this study did not confirm that.
There were found some confounding and random variables, which could easily distort the results. The experiment was conducted in one computer room, where the 54 participants carried out the experiment in the same time. The computers and the participants produced a high noise level, which was interrupting. Another factor that could influence the results, were the consistency of the participants. There were some international students among the participants, who could show a slower performance on the Stroop 2 task, nevertheless they scored low in the personality test for inattention and impulsivity. This assumption is based on previous studies, which found interference between the two languages of bilinguals whilst completing the Stroop 2 task (Preston and Lambert, 1969; Dyer 1971).
Another possible answer to the question, why there were found no correlation between the performance on the Stroop 2 task and inattention, can be found in the data analysis. For the correlations with concern to Stroop 1 test were analysed by the parametric Pearson’s r test, whereas correlations with the Stroop 2 test were analysed by the less powerful non-parametric Spearman’s rho test. The fact that the performance on the latter task showed a non-Gaussian distribution, which may have been caused by the interference of the noise level in the experimental room, or the bilingual students’ scores, or both. This finding indicates that the results of the experiment may have been more reliable if the participants had undertaken the tasks in a quite environment with an experimenter not participating with the provision of data; and if the bilingual students had been excluded from the experiment. Then there would be a higher possibility to that the test results may support the hypotheses.
The personality questionnaires were filled out by the participants (self-report) and were relatively short, which could lead a not accurate measure of inattention or impulsiveness. This weakness of the study may have contributed to a Type II error too.
Conclusion
A correlation between the performance on the Stroop 1 task and the personality factor of inattention was found to be significant; the other three hypotheses were not supported. As previous studies have supported the hypotheses, supposedly the method of the data collection contributed to the non-significant results. Further investigations are suggested to explore whether or not there is an association between the two types of Stroop tasks and the two personality factors, which both are inhibiting factor in learning and performing on tests and exams.
References
Alansari, B. (2004). The relationship between anxiety and cognitive style measured on the Stroop test. Social Behavior and Personality. 2004.
Block, J. (1993). Study personality the long way. In D.C. Funder, R.D. Perke, C. Tomlinson-Keasy & K. Widama. Studying lives through time: Personality and development. (pp 9-41). Washington DC: American Psychological Association.
Broadbent, D.E. (1958). Perception and communication. Oxford: Pergamon Press.
Clark, M.S. & Fiske, S.T. (1982). In K. McClelland (1992). Perceptual Control and Sociological Theory. [Online] Available:
Deutsch, J.A. & Deutsch, D. (1963). Attention: Some theoretical considerations. Psychological Review, 70, 80-90.
Doehrman, Landau, & O'Connell (1978). In B. Alansari (2004). The relationship between anxiety and cognitive style measured on the Stroop test. Social Behavior and Personality.
Dyer, F.N. (1971). Color-naming interference in monolinguals and bilinguals. Journal of Verbal Learning and Verbal Behavior, 10, 297-302.
Eysenck, M.W. & Keane, M.T. (ed) (2000). Cognitive psychology: a student’s handbook. Hove: Psychology Press.
Kahneman, D. (1973). Attention and effort. Englewood Cliffs, NJ: Prentice Hall.
MacLeod, (1991). In B. Alansari (2004). The relationship between anxiety and cognitive style measured on the Stroop test. Social Behavior and Personality.
Norman, D.A. (ed)(1976). Memory and attention. Chichester: Wiley.
Preston, M.S., Lambert, W.E. (1969). Interlingual interference in a bilingual version of the Stroop color-word task. Journal of Verbal Learning and Verbal Behavior, 8, 295-301.
Schiller, P.H. (1966). Developmental study of color-word interference. Journal of Experimental Psychology, 72, 105-108.
Stroop, J.R. (1935). Interference in serial verbal reactions. Journal of Experimental Psychology. 18, 643-661.